This is the season for these rich, alcoholic brews -- which would put you out of commission pretty fast if you quaffed them at a thirsty summer picnic (though the Belgians somehow manage to drink their saisons and bieres de garde in summer). It's traditional to sip them slowly in the evening during the darker, colder seasons of the year. "Winter warmers," a lot of people call them.

Nearly all age-worthy beers are ales, and they're particularly dark ones. Unlike porter or stout, which get their color from being made from roasted malts, these are dark because they have a particularly high concentration of malt. They're the equivalent of a highly "extracted" wine, because they use up to three times as much malt per gallon as regular beer.

In effect, they're a concentrate of beer. This gives them what winemakers call structure. Along with strong extract, they contain plenty of hops, a preservative, and up to three times as much alcohol as ordinary beer. So while an everyday lager starts to go bad after about three months, these rich, strong, almost syrupy brews have the stuffing to survive and even improve for years.

Barley wines are the most alcoholic and age-worthy of the strong ales, some of them reaching 14% or 15% alcohol. Christmas or winter ales are seasonal releases. The spices they contain are not only festive but can add to the interest as they age. Abbey ales, bieres de garde and saisons are Belgian and French styles also made by American craft brewers. (See box.)

The idea of age-worthy beers may seem exotic, but that's bound to change. Anheuser-Busch recently joined the trend -- started in this country by Anchor Brewing's Old Foghorn 30-odd years ago -- by issuing its own 8.5% alcohol beer, Brew Masters' Private Reserve, which is vintage-dated and comes in the sort of large bottle used by many Belgian ales intended for aging.

But on second thought about that holiday gift idea, if your friend doesn't have a sense of humor, maybe you should think twice before getting out the wrapping paper. West Coast brewers lavish their weirdest, most extreme names on their strongest, most age-worthy beers: Bigfoot, Old Crustacean, Old Numbskull, Double Bastard. Not to mention Hairy Eyeball and its even grosser cousin Eye of the Hairball.

They're all luscious beers, mind you. On the other hand, when you give wine, you never have to explain not to take the name on the bottle personally. (Unless that's what you intend, of course. Robert Rogness at Wine Expo in Santa Monica tells of a customer who sent an extra-large bottle of Double Bastard Ale to her soon-to-be ex-husband.)

A quirky business

THOUGH these beers still represent a small fraction of beer sales, craft brewers consider them the highest achievement of their art and relish the challenge of making them.

"Barley wine is a quirky beer to make," says Greg Koch, chief executive of Stone Brewing. "It stresses the brewery to the maximum -- it pushes the limit of bitterness and alcohol." Ordinary beer is fermented for a week or so, but a barley wine such as Stone's Old Guardian often spends months in the fermenter in order to convert all possible sugar into alcohol. Brewers have little tricks to keep the fermentation going, such as rolling barrels around to "wake up" the yeast.

Unlike, say, a young Cabernet, these strong beers are always drinkable when released. Tasters find malt and hop flavors in them, obviously, and also fruits, spices, fresh bread ... you can feel them struggling to describe the seductive flavors that slowly emerge from the powerful maltiness.

What happens when the beer ages? It depends on what kind you're talking about. The lighter ones become rounder and mellower, while the really strong ones develop totally new flavors, the way wine does.

Sierra Nevada Brewing's brew master Steve Dressler says his Bigfoot Barleywine Style Ale acquires sherry notes with age. "The hops really subside -- they're the first thing to go -- and the malt becomes more pronounced. It develops some dried-fruit, raisiny type flavors and aromas, and you get a sweeter maltiness. It's more like a Port than a beer by that time." Some people detect more exotic flavors such as chocolate and tobacco in old barley wines.

Sang Yoon, owner of Father's Office in Santa Monica, has been tasting aged Anchor Christmas Ale for years. "Every year it's a different recipe, and [the vintages] change over time. They start out really powerful, bright and spicy, then they become nutmeg-y and nuanced, then cocoa notes come out."